Conventionally, the printing (application) of a magnetic substance (magnetic ink) onto paper money and the like in the prescribed pattern has been practiced. For example, banking machines including automated teller machines and the like, dispensers, and ticket-vending machines detect the condition of the magnetic substance provided in the prescribed pattern to paper money dropped in each machine or the like by using a magnetic sensor built in each machine, and makes a determination as to whether the paper money or the like is real or false from a magnetic pattern that is detected.
A magnetic sensor of this type uses, for example, a magneto-resistive element (magneto-resistive effect element: MR element). This magnetic sensor catches a change in a magnetic field and the presence of a magnetic substance as a change of the electric resistance value of the magneto-resistive element. To this end, in the magnetic sensor using a magneto-resistive element, the magnetic biasing for providing magnetic flux beforehand to the magneto-resistive element with a permanent magnet is carried out. The magneto-resistive element is used in an area where the strength of the magnetic field and the resistance value have a linear relationship due to the magnetic bias.
A magneto-resistive element of this type has high temperature dependency. For this reason, two magneto-resistive elements are used in a serially-connected state for the purpose of counteracting the temperature dependency. To be specific, in a magnetic sensor disclosed in Unexamined Japanese Patent Publication No. 6-18278, two (a pair of) magneto-resistive elements 1a and 1b are connected in series with each other through an electrode 2 as illustrated in FIG. 1A. A common connection point P of the electrode 2 serves as a detection terminal. The magneto-resistive elements are provided with flux (magnetic biases) having the same magnetism, which are emitted from a magnet 5. In an electric equivalent circuit shown in FIG. 1A, the two magneto-resistive elements 1a and 1b are connected in series with each other as illustrated in FIG. 1B, and voltage of a DC power source 3 is given to between both ends thereof. Further connected to the electric equivalent circuit is an amplifier 4 for amplifying the potential level of the common connection point P of the magneto-resistive elements 1a and 1b. A potential change signal of the common connection point P, which is amplified by the amplifier 4, is transmitted to a detector 8 for discriminating, for example, the kinds of paper money.
According to this magnetic sensor, DC voltage is applied to between both terminals of the serially-connected magneto-resistive elements 1a and 1b by using the DC power source 3. The amplifier 4 amplifies the potential change of the common connection point P of the magneto-resistive elements 1a and 1b. The magnetic sensor detects the condition (pattern) of the magnetic ink (magnetic substance) printed, for example, on paper money, from the amplified potential change. In other words, this magnetic sensor moves a detection subject S on which a magnetic substance M is printed while bringing the detection subject S close to the magneto-resistive elements 1a and 1b, to thereby detect the condition (pattern) of the magnetic substance M.
For instance, FIG. 1A shows that the detection subject S on which the magnetic substance M is printed in stripes is brought close to the magneto-resistive elements 1a and 1b of the magnetic sensor, and at the same time it is moved at the prescribed speed in the direction intersecting the flux emitted from the magnet 5. As illustrated in this figure, the more the magnetic substance M printed on the detection subject S approaches the magneto-resistive element 1a, the more the flux emitted from the permanent magnet 5 converges upon the magnetic substance M. As a result, the flux passing through the magneto-resistive element 1a grows larger. That is to say, the resistance value of the magneto-resistive element 1a is increased, which lowers the potential of the common connection point P.
When the magnetic substance M draws apart from the magneto-resistive element 1a while getting close to the magneto-resistive element 1b, the flux passing through the magneto-resistive element 1a is decreased. Accordingly, the magneto-resistive element 1a is reduced in its resistance value. At the same time, the magnetic substance M approaches the magneto-resistive element 1b, and the flux passing through the magneto-resistive element 1b grows larger. At this point, the resistance value of the magneto-resistive element 1b is increased. This raises the potential of the common connection point P.
On that account, the potential of the common connection point P is, as illustrated in FIG. 1A, gradually reduced as the magnetic substance M printed on the detection subject S in stripes approaches the magneto-resistive element 1a. On the other hand, as the magnetic substance M draws apart from the magneto-resistive element 1a and gets close to the magneto-resistive element 1b, the potential of the common connection point P is increased by degree. When the magnetic substance M draws apart from the magneto-resistive element 1b, the potential of the common connection point P returns to the potential in the initial state. Basically, in magneto-resistive element 1b having the above structure, the potential of the common connection point P has a value different from that of the potential in the steady state along with the displacement of the magnetic substance M. To be concrete, in response to the displacement of the magnetic substance M, the potential of the common connection point P is brought into the state lower than the potential in the steady state (when the magnetic substance M applied to the detection subject S approaches the magneto-resistive element 1a) and the state higher than the potential in the steady state (when the magnetic substance M applied to the detection subject S approaches the magneto-resistive element 1b).
The potential is brought into the low state and the high state along with the displacement of the detection subject on the basis of the potential in the steady state at the common connection point of the serially-connected magneto-resistive elements. This causes the problem that the magnetic sensor for detecting the width of the magnetic substance printed on the detection subject has to include an intricate detection circuit. Moreover, when the front or rear edge of the detection subject reaches the magnetic sensor, the potential is in the low state and the high state. On the other hand, the potential during the magnetic substance passes above the magnetic sensor is equal to the potential without the magnetic substance. As a consequence, there has been the problem that the magnetic sensor has difficulty even in detecting the concentration of the magnetic substance printed on the detection subject.